The present invention relates to implantable spinal devices and methods for their use. More particularly, the present invention relates to interbody devices formed of bone that may be utilized in spinal fusions.
A variety of interbody implants are available for spinal fusion procedures. These implants have been manufactured of various materials including steel, titanium, composites, allograft, xenograft or other biocompatible materials, and have the necessary strength to prevent the disc space from collapsing before fusion has occurred. Other techniques for spinal fusion include the placement of bone graft material in the disc space along with a plate or rod construct that spans the affected disc space. One disadvantage to the above devices is that once fusion has occurred, the implants and hardware used to maintain the stability of the segment is unnecessary and remains in the body as a foreign object.
Other types of implants have been developed from bio-compatible metals which incorporate threads on the outer surface of the implant that retain the implant in the disc space after it is threaded therein. Still other implants have been developed that are made from bone. Examples of such spacers made from bone having use in spinal procedures are disclosed in U.S. Pat. No. 5,989,289. The spacers in the ""289 patent are provided with vertebral engaging surfaces on the upper and lower faces of the implant to resist migration of the implant in the disc space and/or expulsion of the implant from the disc space. While spacers made of bone offer much improved incorporation in fusion procedures, the inherent brittle nature of bone resulting from a high mineral content, particularly load-bearing cortical bone, severely limits its potential for use in applications that require the implant to resist loading other than bearing or compression type loading. For example, cortical bone typically consists of approximately 70% mineral content and 30% non-mineral matter. Of this non-mineral matter, approximately 95% is type I collagen, with the balance being cellular matter and non-collagenous proteins.
Bone grafts have commonly been used in a fixed shape, pulverized, or as pliable demineralized bone. One form of a pliable bone graft is a demineralized bone material typically in the form of a sponge or putty having very little structural integrity. While a demineralized bone segment may retain properties suitable to support bone ingrowth, the structural properties of the bone are altered by removal of its mineral content. Thus, such bone sponges and putties may not typically be used in load-bearing applications.
Therefore, there remains a need for bone implants having the requisite load carrying capabilities for applications that require both bearing or compression load carrying capabilities along with capabilities for resisting loading other than bearing or compression type loading.
The present invention is directed to a bone implant having a rigid portion for insertion between adjacent bony structures and a flexible portion for securement to the adjacent bony structures.
According to one aspect of the invention, there is provided an implant that has a body portion positionable in the disc space between adjacent upper and lower vertebrae. The implant further includes an upper member and a lower member extending from the body portion along the upper vertebral body and the lower vertebral body, respectively. The body portion, the upper member, and the lower member are each made from bone material.
According to another aspect of the invention, there is provided an implant that includes a bone body with a first bearing surface and a second bearing surface. An upper bone member extends from the body in a first direction and a lower bone member extends from the body in a second direction opposite the first direction. The upper and lower bone members are at least partially demineralized and flexible.
According to a further aspect of the invention, there is provided a spinal fusion implant that is adapted for insertion into the space between adjacent first and second vertebral bodies. The implant includes a bone body having a first bearing surface for contacting an endplate of the first vertebral body and a second bearing surface for contacting the endplate of the second vertebral body. At least one flexible portion extends from the bone body so that it can be secured to one of the first or second vertebral bodies outside the disc space.
According to yet another aspect of the invention, there is provided a method of preparing a bone implant. The method includes providing a rigid bone segment having a body portion with an upper bearing surface and opposite lower bearing surface. The rigid bone segment further includes an upper flange member and an opposite lower flange member that each extend from the body portion. The upper and lower flange members are at least partially demineralized so as to be flexible.
According to another aspect of the invention, there is provided a method of inserting an interbody fusion implant made of bone. The method includes: providing an implant formed of bone and having a body portion with an upper bearing surface and opposite lower bearing surface, the rigid bone segment including a flexible upper flange member and an opposite flexible lower flange member each extending from the body portion; accessing the disc space between adjacent vertebrae; inserting the body portion of the implant into the disc space; securing the flexible upper flange member to the upper vertebra; and securing the flexible lower flange member to the lower vertebra.
According to a further aspect of the invention, a method of preparing a bone implant, is provided. The method includes obtaining a rigid bone segment and forming from the rigid bone segment an implant having a body portion with an upper bearing surface and opposite lower bearing surface, the rigid bone segment further including an upper flange member and an opposite lower flange member each extending from the body portion.
These and other aspects, advantages, features, embodiments, and objects of the present invention will be apparent to those skilled in the art based on the following descriptions of the illustrated embodiments of the present invention.